Thermal spray technologies, e.g., plasma spray, flame spray, and the like, have been employed to apply various coatings, such as ceramic coatings, to an article. For example, European Patent No. 0825272 to Nakagawa et al. describes a high speed thermal spray coating method. In this process, a high speed flame is produced using a combustion gas and then thermal spray coating material powder is sprayed by a flame gun into a receiving surface of a base material using the high speed flame. U.S. Pat. No. 6,386,140 to Müller et al. illustrates an example of a plasma spray apparatus.
The process for using a plasma spray apparatus or flame spray apparatus to apply a coating to an article typically entails disposing the article in a nest. The nest holds and masks the article such that only the desired area of the article will be coated during the spraying process. In a flame spray process, ceramic powders, for example, are then heated to temperatures of up to about 2,000° C. while they are sprayed at the article.
In some applications, e.g., to flame spray coat an oxygen sensor with a ceramic (at ceramic material temperatures of about 2,000° C.), copper-aluminum-bronze nests have been found to be particularly useful. Unfortunately, however, for processes, e.g., plasma spray processes, where the ceramic material can strike the article and nest at temperatures of up to about 6,000° C. and possibly greater, copper-aluminum-bronze nests have the disadvantage that the ceramic material adheres to the nest, and the nest can melt, oxidize, or otherwise degrade and fail. Additionally, adhesion of the coating material to the nest changes the nest size and consequently the area masked by the nest. As a result, the nest requires regular cleaning in order to maintain reproducibility in the coating process and to attain coated articles that meet the desired specifications. For example, bronze nests used under these conditions require cleaning every approximately 30 minutes. Since the ceramic forms a hard coating on the nest, cleaning can be difficult, time consuming, and can damage the nest. For instance, cleaning can comprise striking the nest with an object (e.g., a hammer or similar tool) to crack and enable removal of the coating. Alternatively, the nest can be plunged into liquid nitrogen to crack and remove the coating. Another coating removal technique comprises grit blasting the nest. All of these techniques adversely effect the structural integrity and geometry of the nest. Since the nest acts as a mask (e.g., similar to a stencil), maintenance of the size and geometry of the nest is important in attaining reproducible coating applications.
In order to avoid some of the disadvantages of metal or alloy nests, disposable nests are utilized in some applications, such as in the aerospace industry. For example, various airline components (stators, blades, and the like) are masked with a tape (e.g., a Nextel® tape). Application and removal of the tape is a manual, time consuming process. Additionally, since it is a manual process, the precision of the application of the tape is affected by human error, and the cost of this process is not only a function of the coating materials but also of the labor costs and the fact the masks are disposable.